Mimetic biosensors composed by layer-by-layer films of phospholipid, phthalocyanine and silver nanoparticles to polyphenol detection
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Highly selective and sensitive modified electrodes have been the focus of many studies in sensing applications. Gene or enzymatic biosensors are greatly effective in this context, but they are often fragile and expensive. An alternative to these systems is the use of mimetic systems such as artificial enzyme immobilized in a matrix formed by thin films, for which the electrostatic layer-by-layer (LbL) technique has been widely applied. Here, the formation of bilayers or trilayers combining a cationic electrolyte (poly(allylamine) hydrochlorate, PAH), an anionic metallic complex (iron tetrasulfonated phthalocyanine, FeTsPc), an anionic phospholipid 1,2-dipalmitoyl-sn-3-glycero-(phosphor-rac-(1-glycerol), DPPG) and silver nanoparticles (AgNPs) arranged as (PAH/FeTsPc + DPPG)n and (PAH/FeTsPc + DPPG/AgNP)n was structurally and morphologically characterized. The electrostatic interaction of PAH, FeTsPc, and DPPG molecules were identified as the driven forces that allow the LbL film growth. The incorporation of AgNPs in the LbL films makes possible to active the surface enhanced resonant Raman scattering (SERRS) effect. The LbL films were evaluated as a sensor to catechol by cyclic voltammetry and impedance spectroscopy. The presence of AgNPs enhances the electrocatalytic activity of FeTsPc in the film to catechol oxidation. The (PAH/FeTsPc + DPPG/AgNP)5 LbL film presented a linear concentration range for catechol detection from 2 up to 100 μM, with a limit of detection of 0.87 μM. The distinction of catechol concentrations as well as discrimination among catechol, gallic and vanillic acid aqueous solutions was efficiently performed by principal component analysis (PCA) from impedance spectroscopy measurements. The LbL films here evaluated showed suitable properties to be applied as mimetic biosensors. The sensor was applied to polyphenol determination in green tea samples by standard addition showing high selectivity to catechol compared with results from Folin-Ciocalteu method.